Liquid crystal display devices have recently been used in a wide range of devices including small electronic devices such as cellular phones as well as in large electronic devices, such as personal computers and televisions, and the application range thereof has been gradually widened. Since such Liquid crystal display devices are not self-luminous, generally, a light source such as a backlight unit is disposed at one side of a lower polarizing plate located below a liquid crystal cell, and light emitted from the light source is directed to pass through the liquid crystal cell to display images.
Liquid crystal display devices having high levels of brightness can display brighter images. In addition, Liquid crystal display devices having high levels of white brightness can have high contrast ratios, and thus, can display clear images. Therefore, a large amount of research has been actively conducted into improving the brightness of Liquid crystal display devices.
In the related art, a method of decreasing the content of iodine in a polarizer has been proposed as a method of improving the brightness of Liquid crystal display devices. However, the proposed method may result in a decrease in the degree of polarization. Furthermore, in other techniques proposed for improving light use efficiency, a reflective polarizing plate is disposed around a lower polarizing plate, and light emitted from a backlight unit but having a polarization state unnecessary for the lower polarizing plate is selectively reflected by the reflective polarizing plate toward a reflective plate of the backlight unit so that the light can be re-reflected. However, these techniques require additional processes and relatively expensive materials.
In general, an air gap exists between a lower polarizing plate and a backlight unit of a Liquid crystal display device and, due to a difference in refractive indices between the air gap and the lower polarizing plate, light may be reflected. Due to such a reflection of light, the amount of light emitted from the backlight unit and incident on the lower polarizing plate is reduced to result in a decrease in brightness. Although the existing brightness improving methods described above can be used to increase light use efficiency, the existing brightness improving methods can not be used to prevent a decrease in brightness such as that caused by an air gap.
Therefore, a new technique is needed for improving the brightness of a Liquid crystal display device by preventing a decrease in brightness caused by an air gap between a lower polarizing plate and a backlight unit.